1. Field of the Invention
The present invention relates to a flat panel display, and more particularly, to a method and apparatus for controlling picture quality of a flat panel display capable of electrically compensating for a display defect which appears on a display panel.
2. Discussion of the Related Art
Examples of a flat panel display include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP) and an organic light emitting diode display (OLED), most of which have been put to use and are commercially available.
Since the LCD satisfies trends of electronic appliances such as lightness, thinness, compactness and smallness and has excellent mass productivity, cathode ray tubes have been rapidly replaced with LCDs.
In particular, an active matrix type LCD which drives liquid crystal cells using thin film transistors (hereinafter, referred to as “TFTs”) has excellent picture quality and low power consumption and has been rapidly developed to realize a high resolution and increase in screen size of a device by a recent mass production technology and the results of research and development.
In most of the flat panel displays, a photolithography process is used in a manufacturing process for patterning fine signal lines or electrodes of a pixel array. The photolithography process includes exposure, development and etching processes.
In the photolithography process, due to variation in an amount of exposure light, a display defect (display spot) having brightness and chromaticity different from those of a normal display surface may appear in a process of testing a completed display panel. The display defect is caused by an overlapping area between a gate and a drain of a TFT, the height of a spacer, parasitic capacitance between signal lines, and parasitic capacitance between the signal line and a pixel electrode, which become different from those of the normal display surface due to the variation in amount of exposure light in the photolithography process.
FIGS. 1 and 2 are respective views showing cases where a vertical line defect and a horizontal line defect are included in the display defect.
As shown in FIGS. 1 and 2, an exposure apparatus used in a process of simultaneously forming a plurality of pixel arrays A1 to A18 or B1 to B6 on a large mother substrate includes a multi-lens in which a plurality of lenses 10 are arranged in two rows and overlap each other with a predetermined width GW. In the pixel arrays A1 to A18 or B1 to B6, a plurality of data lines and a plurality of gate lines intersect each other, TFTs are formed at the intersections, and pixel electrodes are arranged in a matrix. In the pixel arrays A1 to A18 or B1 to B6, columnar spacers for holding a cell gap may be formed. The pixel arrays A1 to A18 or B1 to B6 are divided by a scribing process. In FIG. 1, arrows and numerals represent scan directions and scan sequences of the lens 10. That is, the multi-lens of the exposure apparatus sequentially exposes the pixel arrays A1 to A18 or B1 to B6 while moving from the right side to the left side, from the left side to the right side, from the right side to the left side after moving upward, from the left side to the right side, from the right side to the left side after moving upward, and from the left side to the right side.
The lenses 10 of the exposure apparatus have respective aberrations and the aberrations of the lenses are different from one another. Accordingly, the amount of received light and the light distribution of photoresist coated on the mother substrate 12 vary according to the positions of the lenses 10 and the overlapping width of the lenses 10. Due to the variation in amount in exposure light of the photoresist according to the positions of the lenses 10 and the overlapping width GW of the lenses 10, the photoresist pattern after the development process varies according to the positions of the lenses 10 and the overlapping width between the lenses 10. As a result, the overlapping area between the gate and the drain of the TFT partially varies in the display surface of the pixel arrays A1 to A18 or B1 to B6, a pixel voltage varies according to the positions of the display surface, the heights of the columnar spacers of the pixel arrays A1 to A18 vary according to the positions of the display surface, and the cell gap partially varies. When all the manufacturing processes are completed after scribing the pixel arrays A1 to A18 or B1 to B6 and the same data is applied to all the pixels of the flat panel display, the display defect appears in the form of the vertical line or the horizontal line. The display defect appears to extend in a movement direction of the multi-lens of the exposure apparatus, and the vertical line and the horizontal line vary according to the movement direction of the multi-lens 10 or the arrangement direction of the pixel arrays A1 to A18 or B1 to B6 arranged on the mother substrate 12. For example, if 18 small pixel arrays A1 to A18 are vertically arranged on the mother substrate 12 as shown in FIG. 1, vertical lines appear in the pixel arrays A1 to A18. As shown in FIG. 2, if six middle/large pixel arrays B1 to B6 are horizontally arranged on the mother substrate 12, horizontal lines appear in the pixel arrays B1 to B6.
The display defect appears to extend in the movement direction of the multi-lens of the exposure apparatus in the form of the vertical line or the horizontal line, and the vertical line and the horizontal line vary according to the movement direction of the multi-lens or the arrangement direction of the pixel arrays arranged on the mother substrate.
In order to solve the display defect in the form of the vertical line or the horizontal line, conventionally, a method of examining precision of a photomask to improve the mask or regulate the arrangement of the multi-lens has been used. However, a phenomenon that the vertical line or the horizontal line appears cannot be prevented by this method. In order to overcome the limitation of the prior art, the present applicant suggested a method of selecting data to be displayed in a display defect region and compensating for the brightness of the display defect region by the modulation of the data, which is disclosed in Korean Patent Application No. 10-2006-0059300.
However, since the vertical line defect and the horizontal line defect have different brightness distributions, it is difficult to compensate for the brightnesses of the defects, which appear in different forms, by a method for compensating for a defect which appears in any one form.